To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Starting price: 350 euros.
2. Current condition: 25 (BC), indicating that the coin is in quite low condition.
3. Auction history:
- In 2020, the coin was auctioned with a starting price of 225 euros and sold for 320 euros, with a condition of 70.
- In 2024, it will be auctioned with a starting price of 450 euros and an estimated price of 500 euros, with a condition of 75.

Given that the current condition of the coin is significantly lower (25) than the conditions of the previously auctioned coins (70 and 75), this will negatively affect its value.

The average hammer price of the coin in the past has been 350 euros, but since the current condition is much lower, it is reasonable to adjust the price downward.

Considering all these factors, an estimated maximum purchase price could be between 150 and 200 euros, as the condition is a critical factor that reduces the value of the coin compared to previous auctions.